1. Field of the Invention
The present invention relates to a wireless resource assigning apparatus and a wireless resource assigning method for assigning wireless resources efficiently when users can use multiple wireless resources that can be used for wireless communications.
2. Description of the Related Art
Algorithms for enhancing frequency efficiency in a single frequency band have been studied from the past. As an algorithm for power assignment for a single user, a transmit power control method is proposed for assigning large power to a sub-carrier in a good channel state and assigning small power to a sub-carrier in a bad channel state (refer to non-patent document 1, for example). In addition, a scheme is proposed for largely enhancing throughput by combining this technology with another technology such as adaptive modulation and coding, and the like (refer to non patent document 2, for example).
On the other hand, a multi-user scheduling algorithm is proposed (refer to non patent document 3, for example). The RR (Round Robin) method is a scheduling algorithm for assigning resources fairly. According to this method, although fairness can be kept, SINR (Signal to Interference and Noise power Ratio) is not considered. Thus, compared with a scheme considering SINR, the system throughput is low. The Max. CIR (Maximum Carrier to Interference power Ratio) method is an algorithm for maximizing the system throughput by assigning the radio resource to a user who has the maximum SINR. In this scheme, since the communication opportunity is not given to a user having low SINR, there is a problem that fairness cannot be kept. The PF (Proportional Fairness) method is an algorithm for assigning the radio resources to a user who has the maximum instantaneous SINR normalized by an average SINR of the user in order to keep fairness among users. Thus, the system throughput can be improved compared with the RR method while keeping fairness.    [Non-patent document 1] R. F. H. Fischer and J. B. Huber, “A New Loading Algorithm for Discrete Multitone Transmission”, Proc. IEEE GLOBECOM 1996, Vol. 1 pp. 724-728, 1996;    [Non-patent document 2] T. Yoshiki, S. Sampei, N. Morinaga, “High bit rate transmission scheme with a multilevel transmit power control for the OFDM based adaptive modulation systems”, TRANSACTIONS OF IEICE, Vol. J84B, July 2001;    [Non-patent document 3] Y. Ofuji, S. Abeta, M. Sawahashi, “Fast packet scheduling algorithm based on instantaneous SIR with constraint condition assuring minimum throughput in forward link”, TECHNICAL REPORT OF IEICE, RCS2002-75, pp. 1-6, June 2002.
Aforementioned algorithms exist as conventional multi-user scheduling algorithms. But, they are assumed to be used in a single wireless resource, and algorithms for multiple wireless resources are not considered. Thus, there is a problem that an effect of scheduling cannot be obtained when multiple wireless resources are targeted.
FIG. 1 shows a conventional method for assigning wireless resources. Since the target for multi-user scheduling is limited to a single wireless resource, a part of users that are targets are specified (roughly assigned) after selecting wireless resources in step S10. Next, multi-user scheduling is performed for each wireless resource independently (steps S11-S1N).
It is generally known that the larger the number of users is, the higher the effect of scheduling of the conventional multi-user scheduling is. However, as mentioned above, since multi-user scheduling is performed after a part of users are assigned to each wireless resource, the number of users using the wireless resource becomes small, so that the effect of the scheduling is decreased. Therefore, it becomes difficult to perform wireless resource assignment that follows channel state and interference amount in multiple wireless resources.